Dude, that's just not fair. A low blow to my thread. I am not a psychiatrist but the obvious suggesstions would be:
vis-a-vis you friend: Buy flowers, show your support. Show up. Listen. Try to talk as little as possible (especially during the eulogy); grieving people tend to want to vent and be listened to. They know the good qualities of their loved ones and the crock it is having them go so early, etc... Like women, they just want you to listen, not offer advice and/or help. Good phrases : "I am here whenever you need me" and "I'm so sorry." Bad phrases: "Only the good die young" and anything invoking "God's will".
As for your cousin : Keep a positive attitude and keep people focused on the problem at hand when they start to stray or break down. "so and so needs us to be strong now". And hire a PI immediately; they are WAY better than the cops. You want to find a doughnut- call a cop, want to find a person, call a good PI. At the same time you must also be prepared for the worst.
Look at this, you've turned this into a "Dear Abby" thread.